1. Field of the Invention
The present invention relates to a document feeder which is used while being incorporated in an electrostatographic copier, for example, to feed original document sheets successively to a reading region.
2. Description of the Prior Art
Conventional optical reading apparatuses which read information from the surface of a document optically by applying light through a slit, such as electrostatographic copiers, employ first exposure mode where a fixed document is read by a moving optical system, or second reading mode where a moving document is read by a fixed optical system. In the second exposure mode, a recirculating document feeder (called RDH hereafter) may be employed which feeds original document sheets to a reading region successively one by one and, after exposure-reading, returns the original sheets to the initial position.
FIG. 1 is a simplified sectional drawing of RDH 1 of the prior art. RDH 1 which is a typical prior art comprises a document hopper 3 where original sheets 2 to be copied are stacked, a support cylinder 5 of a straight cylinder shape which carries the original 2 to make it pass through a reading region 4, and an original transport path 8 comprising a transport path 6 to transport the original from the document hopper 3 to the reading region 4 and a transport path 7 to return the original from the reading region 4 to the document hopper 3. Originals 2 stacked in the document hopper 3 to be copied are supplied by a feed roller 9 onto the transport path 6, one sheet at a time from the top of the stack. The original 2 transported through the transport path 6 is supported by the support cylinder 5 and passes over a transparent plate 10 made of hard glass or the like which is installed in the reading region 4. The surface of the original 2 passing over the transparent plate 10 is exposed to light from an exposure lamp of the optical system which is not shown in the drawings to read the image of the original, and copy process is carried out in the copier. The original 2 whereof the image on one surface has been read is transported through the transport path 7 and is placed at the bottom of the original sheets 2 stacked in the document hopper 3.
Every time the original 2 is fed from the document hopper 3 and returned through the reading region 4 to the bottom of the document hopper 3, relation of the top and bottom faces of the returned original 2 is inverted from that before being fed. That is, one surface of the original 2 which faced upward in FIG. 1 when being fed from the document hopper 3 faces downward when the original 2 is stacked in the document hopper 3 after passing the reading region 4. Copy of both sides of the two-sided originals, which carry information recorded on both sides of each sheet, onto corresponding surface of copy paper, namely duplex copy is carried out as follows. When one surface of a sheet of the original is read, the original is returned to the document hopper 3, where the original is stacked with the surface which faced upward before copying now facing downward. Therefore, in case of paper jamming in the transport path 6 after the original 2 has been fed again from the document hopper 3 to read another surface of the original 2 which has not been read, the original 2 may be stacked again without noticing that the original 2 is inverted from the face-bottom direction at the time of the initial stacking, when returning the original 2 which caused the jam to the document hopper 3, thereby causing the wrong surface to be copied mistakingly, resulting in poor operation performance.
Also according to the constitution of the RDH 1 of the prior art, the original 2 is always fed from the top of the stack of the original sheets in the document hopper 3 to the right in FIG. 1 and is, after reading operation, returned to the document hopper 3 at the bottom of the stacked originals from the right. Consequently, because the mechanism of feeding the original to the transport path 6 and the mechanism of recovering the original from the transport path 7 are concentrated at one side (right-hand side in the case of FIG. 1) of the document hopper 3, structure of the document hopper 3 is complicated on one side.
Further in the RDH 1, the document hopper 3 is made in a configuration of top-feed, bottom-return scheme where the original is fed from the top of the original stack and is returned to the bottom of the stack. The mechanism of returning the original 2 to the bottom of the stacked originals generally tends to become complicated for the reason of precision. Namely, adoption of the top-feed, bottom-return configuration for the document hopper 3 also makes the structure around the document hopper complicated.